Telephone trunk circuits



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J D.Ed 1MM .H RWM L E T Jan. 7, 1930.

A T TRNE Y Patented Jan. 7, 1930 UNITED STATES PATENT oFFicE ROBERT I. D. NICOLL, OF SUMMIT, NEW JERSEY, ASSIG-NOR T0 BELL TELEPHONE LABORATORIES, INCORPORATED, OF NEW YORK, N. Y., A COREORATION OF NEW 'YORK TELEPHONE TRUNK CIRCUITS Application filed June 1,

This invention relates to telephone eX- change systems in which telephone lines, terminating'at different exchanges, may be interconnected by means of trunkcircuits, and more particularly to such systems which employ automatic ringing. cord circuits for makingfconnection with the trunk circuit at the A or originating exchange.

In trunking calls from an A to a B switchboard it frequently happens that the called line, which terminates at the B board, is found to be busy and the B operator therefore-plugs theincoming end of the trunk into a busy back jack instead of the called line.

In cases where the A switchboard is equipped with machine ringing cords having ring back condensers, ringing is automatically started as soon as the cord-circuit is plugged into the trunk and an audible ringing signal goes back-to the calling subscriber, thus indicating that ringing `is going on. With trunk circuits as in use at present if the B operator finds the called line busy and connectsthe inward endof thetrunk to a busy backjack instead of tothe line called, the

subscriber has in the meantime received a false-signal and, upon later receiving the busyfbacktone, is likely to be confused and doubt if the wanted line is really busy for the reason-that. he first heard the'ringing tone.

An object of the invention isto eliminate the possibility, under certain conditions, of giving the calling; subscriber a false indicationofthe progress of his call.

More specifically, the object is to prevent giving a calling subscriber a/'premature audible vringing signal Vwhen the subscribers line is connected to the outgoing end of the trunk circuitby means of an automatic ringing cord circuit before the incoming end of the trunk circuit is connected to the called line.

A feature of the invention, whereby the foregoing object isattained, resides in the provision ofmeans at the inward end of a trunk circuit whereby if the trunk is seized at its outward end by an automatic ringing cord circuit before thekinward end of the trunkis'connected to the called subscribers line the ringing current in the cord circuit will be immediately disconnected and held Serial N0. 282,067.

in this condition until the inward end ofy the trunk circuit is connected to the called line,l at which time the ringing current will be reconnected to signal the called subscriber;

The invention will be understood from thefollowing description when read in connection with the accompanying drawing, which represents two subscribers stations terminating at different exchanges and connected by l means of a machine ringing cord circuit: and

an interoiiice trunk circuit.

`In the drawing the cord circuit C. at eX- change A is what is known as a machine or automatic ringing cord circuit, i. e. one that being accomplished by shunting the normal,

contacts of the ringing relay with condensers of suitable capacity such as condensers 21 and 22.

A call from subscriber X to subscriber Y will now be traced.

l/Vlien the receiver at station X is removed from its hook, lamp l is lighted in response to the usual operation of line relay 2. lVhen the operator in control of cord circuit C inserts the answering plug 3 in jack l of the calling line, cut-off relay 5 operates to restore the line relay 2 and extinguish the lamp l. Supervisory relay 6 also operates, due to the 'fact that the calling subscribers receiver is off the hook, and thereby prevents the supervisory lamp 7 from lighting at this time. Since these circuits are well known' and not a part of the invention, they are only shown schematically for the purpose of giving asofy kus

with the B operator in some manner, such as over a called circuit not shown, and gives the number of the desired subscriber, whereupon the B operator assigns a trunk circuit which we will assume is circuit T. The A operator then inserts'the calling plug 9 of, the cord circuit C in jack 10 of the trunk,

, trunk circuit at its innercontacts but is iinmediately deenergized by the Voperation of tripping relay 13,an operating path for which is prepared when relay 12 operates, which operation will now be described.

Relayl 12 closesobvious circuits to light guard lamp 17 and operate relay 15. Relay 15 thereupon disconnects one'oftheholding Vgrounds from relay 12, which, however, is

not released at this time to release relay 12 due to the normal condition of relay 16.

Relay 12 in operating also connects battery to the Winding of relay 18, thereby completing a circuit for its operation, which can be traced from ground',upper alternate contacts of relay 11, tip conductors of the cord andV trunk uppermost normal contacts of relay 16, `resistance 19, and winding of relay 18 to battery at contacts of relayv 12.

The function of relay 18 is to hold battery disconnected from the ring of the trunk untilV the tip ofthe plug has passed over the'ring Vspring of kthe jack, thereby preventing an annoying click in the operators'receiver due to a surge of current in the upper right hand Y winding of the repeating Icoil at .the moment plug engages the ring spring the tip of the ofthe jack.

When relay 18 operates in response to the operation of relay l2, it locks itself .under control of relay 12 and alsoconnects a battery bridge, including resistances 19 and 20 across the talking conductors of the trunk, thereby causing the tripping relay 13 in the cord to operate.

Relay 13 opens its contacts and removes the short-circuit around relay 26, which relay j thereupon operates in series with relaysll and`12. As soon as relay 26 operates it locks up under control of relay 16 and short-circuits relay 11, which relay releases and disconnects the ringing current from the trunk.

Although it has taken some little vtime to describe the various operations leading up to disconnection of the ringing current in response to plugging into the trunk, the elapsed time involved is only momentary and therel a i i s J A fore no appreciable audible ringing signal 1s passed back to the calling subscriber by way of the condenscrs 21 and 22.

under control of relay 16 pending connection to the called line.' Q

When the B operator inserts plug 23 1n jack 24 of the called line trunk sleeve relay 25 operates, whichextinguishes the guard yand disconnect lamp 17, transfers the tip of-the .cord from the busy test lead to the vcontacts of relay 16 and also operates relay 16.

Ringing is now disconnected and ringing v relay 11 held short-circuited and released Relay 16 disconnects Vthe battery bridge from the trunk and connects the talking conductors of the trunk through to the A operators cord.

When relay 16 operates-.it opens itsinner upper contacts, thereby removing the holding groundV from the winding of relay 12, whereupon relays 12 and 26. release. Relay 16-also opens its inner lower contacts, thusvopeningkr the circuit for relay 15. Relay 15 is slow-ton release and therefore, before it closes its back contacts relay 26 in the cord will have time to release.

When relay 26 releases it removes the shortf circuit around relay 11 and short-circuits` itself.

operation Vof ringing relay 11, which again Y When relay/15 finally releases it reconnects ground at its back contacts to relay 12 and thence over the sleeve circuit to cause the 're connectsringing current-to the trunk which;

this time, is not disconnected until'the called subscriber answers to cause the tripping relay 13 to operate in theusual manner. from this point progresses in the usual -way..^

In case the B operator plugs the trunk into the called line before 'the A operator plugsV into the outgoing end of the trunk, relay25 operates as usual, which in turn operates relay 16 to disconnect the previously mentioned battery bridge including relay 18, thusV preventing the preliminary tripping of ringing when the A operator plugs in as before described. 1 A j Under this latter condition relay 15 does not operate due to operationof relay16 and therefore the momentary opening of thevr trunk sleeveis prevented.

The calll It is evident from the foregoing that when .i Y

the B operator plugsup Vbefore the A operator the automatic yringing equipment functions in the usual manner and is not trippedV until the called subscriberV answers.

In the latter case the guard and disconnect l I lamp 17 is lighted as a guard signal when the B operator plugs in and is extinguished,when

the A operatormakes connection with the,

trunk.

Fromrthe foregoing itis evident that the calling subscriber does not receive an Vaudible signal, which would indicate to him that the dication should be and is prevented by the circuit of this invention.

lVhat is claimed is: 1. In a telephone system, a link circuit, a

, trunk circuit having outward and inward ends, connecting means at the inward end ofV said trunk circuit, means in said link circuit automatically actuated in response to its connection to the outward end of said trunk circuit for applying ringing current thereto, and

means in said trunk circuit responsive to said connection for immediately causing the disconnection of said ringing current and for thereafter reconnecting said ringing current under control of said connecting means at the inward end.

2. In a telephone system, a trunk circuit having outward and inward ends, a link circuit adapted to be connected with the outward end of said link circuit, means at said iink circuit automatically actuated in response to its connection to the outward end of said trunk circuit for applying ringing current thereto, and means in said trunk circuit responsive to said connection for immediately causing the disconnection of said ringing current and connecting means at the inward end of said trunk circuit for causing the said ringing current to be reconnected.

3. In a telephone system, a cord circuit ar ranged for automatically applying ringing current when connected to outgoing lines of certain character, another outgoing line adapted to be seized by said cord circuit,

y means in said other line for preventing more than a momentary application of said ringing current thereto, and means for causing the reapplication of said ringing current to said line in response to a changed electrical condition at the inward end of said other line. v

4. In a telephone system, a rst operators position, a second operators position, lines outgoing from said second position, a trunk line interconnecting said positions, a cord circuit at said rst position arranged to automatically apply ringing current to said trunk when connection is made thereto, and means for immediately disconnecting and thereafter preventing said ringing current from being applied to said trunk line until said trunk line is connected to one of said lines at the second position.

5. In a telephone system, an operators position, a trunk line outgoing therefrom, a machine ringing link circuitf at said position connected to said trunk line, means for disconnecting said machine ringing in response to connect-ion of said link circuit with said trunk line and means for reconnecting said machine ringing to said trunk line under control of connecting means at its inward end.

6. In a telephone system, a link circuit, a trunk circuit, signaling means in said link circuit automatically actuatedupon connection of the link circuit to a line of the trunk circuit, and means in said trunk circuit for disabling said automatic signaling means when the link is connected to the trunk and thereafter reactuating it in response to the actuation of connecting means at the distant end of said trunk circuit.

In witness whereof, I hereunto subscribe my name this 28th day of May, 1928.

ROBERT I. D. NICOLL. 

